How Much ZzzQuil Can You Safely Take?

In our latest question and answer, our pharmacist discusses the dosing recommendations for ZzzQuil Sleep Aid.


I just purchased ZzzQuil to help me get some sleep. It says to only take one cap full but could I double dose without running into any issues? I’m about 350 lbs.

Asked by Kurt On Sep 21, 2022

Answered by
Medical Content Reviewed By HelloPharmacist Staff

Published Sep 21, 2022
Last updated Sep 21, 2022

Key points

  • Most ZzzQuil products contain the active ingredient diphenhydramine, the same ingredient in Benadryl. The Ultra tablets contain doxylamine (an antihistamine similar to diphenhydramine).
  • The adult dose of diphenhydramine is 25 to 50mg, taken every four to six hours. The adult dose of doxylamine is 25mg.


ZzzQuil Nighttime Sleep Aid is a product manufactured by Vicks in multiple formulations including:

  • ZzzQuil Liquicaps
  • ZzzQuil Warming Berry Liquid
  • ZzzQuil Calming Vanilla Cherry Liquid
  • ZzzQuil Soothing Mango Berry Alcohol-Free Liquid
  • ZzzQuil Ultra Tablets

Most ZzzQuil products contain the sedating antihistamine diphenhydramine, the active ingredient in Benadryl. ZzzQuil Ultra tablets contain doxylamine (an antihistamine similar to diphenhydramine). The onset of action of both diphenhydramine and doxylamine is about 30 minutes, and the maximum sedative effects begin 1-3 hours after taking a dose. For most individuals, the duration of action ranges from 4—6 hours.

Liquid ZzzQuil Dosage Recommendations

All liquid formulations of ZzzQuil contain 25 mg of diphenhydramine per 15 ml (one tablespoon). Per the manufacturer, the recommended dose is 30 ml (two tablespoonfuls) at bedtime, which equates to 50 mg of diphenhydramine. When using diphenhydramine as a sleep aid, single doses should not exceed 50 mg per dose. 

ZzzQuil Liquicaps Dosage Recommendations

Each liquicap of ZzzQuil contains 25 mg of diphenhydramine. The recommended dose at bedtime is 2 liquicaps at bedtime, for a total dose of 50 mg.

ZzzQuil Ultra Tablets Dosage Recommendations

Each tablet of ZzzQuil Ultra contains 25 mg of doxylamine. The recommended dose at bedtime is 1 tablet at bedtime, for a total dose of 25 mg.

Additional Information

Diphenhydramine, the active ingredient in ZzzQuil is often used for the treatment of allergies and allergic reactions. in these situations, the dosage recommendation is different versus use as a sleep aid.

Doses up to 100 mg have been safely used for the treatment of allergic reactions. However, as ZzzQuil is purely indicated for use as a sleep aid, dosages should not exceed 50 mg (30 ml). 

Doses above this have the risk of causing a "hangover" effect the next morning and more rarely, paradoxical reactions such as insomnia and restlessness.


About the Pharmacist

Dr. Brian Staiger, PharmD

Dr. Brian has been practicing pharmacy for over 11 years and has wide-ranging experiences in many different areas of the profession. From retail, clinical and administrative responsibilities, he's your knowledgeable and go-to source for all your pharmacy and medication-related questions! Feel free to send him an email at! You can also connect with Dr. Brian Staiger on LinkedIn.

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